Air gun for driving staples or other fastening devices



y 1955 1.. R. CAMPBELL 2,713,165

AIR GUN FOR DRIVING STAPLES OR OTHER FASTENING DEVICES 4 Sheets-Sheet 1 Filed Aug. 24. 1951 s a R w I m x? VH5? m -12 NT, fMxMA k 0 ZMW in rum N w v July 19, 1955 L. R. CAMPBELL F-TAL 2,713,165

AIR GUN FOR DRIVING STAPLES OR OTHER FASTENING DEVICES as it;

M m 0 7/ mai H2 mpfwf m a; a Y B July 19, 1955 1.. R. CAMPBELL ETA!- 2,713,165

AIR GUN FOR DRIVING STAPLES OR OTHER FASTENING DEVICES 4 Sheets-Sheet 3 Filed Aug. 24, 1951 July 19, 1955 1.. R. CAMPBELL ETAL 2,713,165

AIR GUN FOR DRIVING STAPLES OR OTHER FASTENING DEVICES Filed Aug. 24, 1951 I 4 Sheets-Sheet, 4

United States Patent AIR GUN FUR DRIVING STAPLES OR OTHER FASTENING DEVICES Lee R. Campbell, Royal Oak, Frank E. Ebert and Alton Lee Schoening, Detroit, and Le Roy C. Reiterman, Warren, Mich.

Application August 24, 1951, Serial No. 246,491

11 Claims. (Cl. 1-44.4)

This invention relates to a power driven gun, and specifically a gun driven by air for driving staples, tacks, brads, or other fastening devices through readily pierceable material such as upholstery fabrics or the like which it is desired to attach to a foundation backing.

Although thin wire staples have been used for many years for clipping papers together as a part of ordinary oflice practice, it is only comparatively recently that the employment of such staples has spread to industrial uses.

Such staples are used in the form of long strips comprising a large number of individual staples interconnected for convenience in placing them together in a stapling device.

The stapling device, as employed for ofiice use, comprises a combined staple strip magazine and driving head pivotally mounted on a suitable base, the staples being secured together in such way that a strip of staples may be put upon a feeding track of the magazine and by striking the pivotally mounted driving head the staples are detached one by one from the strip thereof and driven through the papers or other materials that it is desired to secure together.

In comparatively recent years, the employement of such staples has spread to industrial uses. As heretofore used industrially, the staple driving device has been hand driven and patterned essentially along the lines of the head of the omce stapling machine removed from the customary base so that it can be used for driving staples or other fastening devices in any desired location. Industrial use of such devices however has not proven satisfactory for use in mass production because of the fatigue factor.

Although some abortive efforts have been made to provide a satisfactory power or air driven stapling gun, such efforts have not, as far as we are aware, proven successful.

Such power driven or air driven stapling guns for industrial uses as heretofore devised have been very complicated and expensive to manufacture due, in part, to the use of many small screws, rivets, or the like, in assembling or connecting the parts, thus making the guns not only expensive and complicated to assemble, but rendering them quite unsatisfactory in use because, due to the rough usage to which the guns are necessarily subjected when used industrially in high-speed production, the assembly screws have tended to become loose, with the resuit that the parts of the guns fall apart. This necessitates frequent repairs with consequent high repair costs and lack of availability of the device during the time required for making the necessary repairs.

We have found after a long period of experimental development work, in order that a stapling air gun work satisfactorily, it is absolutely essential that the air piston which drives the driver, by means of which the staple is propelled through the materials to be fastened together, shall work with a sharp, quick driving action and not a mere pushing action such as characterized many of prior art devices.

Patented July 19, 1955 ice A further important part in the devolpment of a practical air-driven stapling gun for industrial use centers about the constructional details and development of (a) the valve by means of which air is admitted to the air cylinder and piston so as to insure a quick, sharp, positive driving action, as distinguished from a slower pushing action, of the driving element by means of which the staple is detached from the strip thereof and driven through the material to be fastened together; (b) an expansion chamber in the air conduit leading to the valve to act as an accumulator and thus insure an adequate supply of air for obtaining the essential driving action; and (c) the piston and cylinder to which the air under pressure is admitted to provide the driving force.

A further important factor resides in reducing the construction to the simplest possible form in order to reduce to a minimum the manufacturing, construction, and assembling costs and also to insure that the guns will have the greatest possible strength to withstand the rough usage to which they are subjected by the workers, while being of minimum weight for easy handling.

As it is necessary from time to time to use different size staples or other fastening devices, it is highly desirable that the guns be so made as to be readily convertible for use from one size staple to another.

One of the principal objects of the present invention is to provide anew and improved construction of a power unit for an air stapling gun which includes the necessary air conduits and the air piston and cylinder, the valve by means of which air is admitted to the cylinder, in a unitary assembly to and from which any one of a plurality of staple strip magazine units, designed for use with difierent size staples or other fastening devices, may be readily and quickly attached or detached.

A further object of the present invention is to provide a new and improved construction of a cored handle for the power unit which includes the air cylinder and piston, the valve to admit air to the cylinder, and expansion or accumulator chamber, and a single air conduit that serves as both an intake and an exhaust passage by means of which the air passes to and from the cylinder.

Another object is to provide a simplified construction of a valve assembly for the handle unit whereby a single valve and a single air conduit cored in the handle serves to control both the inlet and exhaust of air to and from the air cylinder, the valve being so constructed as to efiect a momentary lag in its movement to full opened position and to provide the time interval essential for a building up of the air pressure available for driving the air piston and thus insure the most eifective driving stroke.

A further object is to provide a new and improved valve assembly consisting of a valve and valve cage or bushing in which a light-weight valve is actuated to its closed position and is held in closed sealing position by the air pressure without requiring the use of additional mechanical means such as valve closing springs, and so that the valve cage and valve may be readily assembled and disassembled for replacement without the use of threads, pins, screws or the like.

'A further object is to provide a new and improved construction and arrangement of the spring means for actuating the staple strip pusher whereby the pusher spring is located out of the line of travel of the strip pusher thereby enabling a longer strip of staples to be used and whereby the same spring means also serves to hold the pusher snugly in contact with the staple track and in engagement with the rear end of the strip of staples.

Another object is to provide a new and improved construction for a track cover which carries a staple strip pusher and the actuating springs therefor, said cover being slidable to an open position to expose the staple track for the insertion of a new strip of staples and so 3 that the strip pusher springs will be properly tensioned by the closing of said cover. 7

A still further object is to provide a new and improved construction of a unitary assembly for a plurality of magazine sections, each of which includes a track designed for the accommodation of one of the many different sized staples or other fastening devices that are to be employed,

the magazine units also including as a unitary part thereof will appear more fully from the following more detailed description and by reference to the accompanying drawings forming a part hereof, wherein:

Fig. 1 is a longitudinal vertical view partly in section of an air-driven gun for driving staples constructed in accordance with the principles of the present invention;

Fig. 2 is a section taken substantially on the line 22 of Fig. 1 of a track section of a staple magazine unit for narrow crown staples;

Fig. 3 is a section similar to Fig. 2 of a magazine track section for wide crown staples;

Fig. 4 is an exploded view of parts of the unit shown in Fig. 3;

Fig. 5 is a sectional detail taken substantially on the line 55 of Fig. 1 showing an enlarged view of the air valve for admitting air to the cylinder and piston and showing the valve in its closed position;

Fig. 6 is similar to Fig. 5 showing the valve in its partially opened position;

Fig. 7 is a horizontal sectional detail taken on the line 77 of Fig. 1 through the cap or closure for the air cylinder;

Fig. 8 is a horizontal section on the line 8-3 of Fig. 1; Fig. 9 is an exploded view of the parts which are combined to make up the magazine and staple driver unit for narrow crown staples;

Fig. 10 is a section on the line 1ti10 of Fig. 1 through the narrow-crown-staple magazine and track unit;

Fig. .11 is an inverted perspective view of the magazine track cover and pusher employed with the narrow crown staples; a

Fig. 12 is an exploded view similar to Fig. 9 showing the parts of a magazine unit employed for wide crown staples; Fig. 13 is a section taken on the line 13-13 of Fig. 3 through the wide-crown-staple magazine unit;

Fig. 14 is an enlarged detail perspective view showing the jamb'plate end of a track section for a wide crown staple;

Fig. 15 is a longitudinal sectional detail through a wide crown magazine unit showing the manner in which the staple strip pusher serves as a stop to limit the opening movement of the track cover; I

Fig. 16 is a perspective view showing the staple strip pusher for the wide crown staples and the means for fastening the end of the pusher spring;

Fig. 17 is a view showing a retaining clip employed for holding the'constituent parts of a magazine and driver unit in assembled condition;

Fig- 18 is a sectional detail through a sheave for the pusher springs on the line Iii-18 of Fig. 4 for the wide crown staples;

Fig. 19 is a side elevation of the structure shown in Fig. 18; and Fig. 20 is a sectional detail showing the construction of a pusher spring retaining tab.

Fig. 21 is a section on the line 2121 of Fig. 1.

'Fig. 22 is a section on the line 22-42 of Fig. 12.

'as at 36, to the handle 2%.

Fig. 23 is a front view of the lower portion of the nose piece shown in Fig. 17 as seen from the right.

The air gun of the present invention, briefly, consists essentially of an assembly of two parts-a combined power and handle unit and a staple strip magazine unit. The handle unit includes an air cylinder and piston, the handle being cored to provide an air expansion chamber and a single air conduit which serves as an inlet and exhaust passage for air to pass to and from the air cylinder and piston under the control of a triggeractuated valve, carried by the handle unit and interposed between the expansion chamber and said conduit. The invention also includes the provision of a plurality of magazine units, each of which is a complete unit assembly separate from the handle unit and which magazine units are constructed in different sizes in accordance with the size of the staple or other fastening device to be driven, each magazine unit being so constructed and arranged that it includes a staple driver assembled with the magazine of the respective size to be used, the various magazine units being interchangeable with, and quickly and readily attachable to and detachable from, the handle unit.

As shown in Fig. l of the drawings, the handle unit consists of a cored handl 20 having at one end thereof a screw threaded inletopening 21 having pipe threads adapted to receive a threaded bushing 22 to receive a hose nipple 23 to which is attached a hose 24 leading to a source of air under pressure.

The hose communicates with an expansion chamber 25, which as shown in Fig. l is of considerably larger crosssectional area than the interior of the hose, cored into the handle and which communicates in turn with a valve chamber 26 into which projects the head of a valve 27. The valve 27 has at its lower end a main stem portion 27a which fits slidably in the bore 23a of a valve bushing 28, that is a snug push fit in a hole 29 drilled into the handle 29. For convenience in manufacturing, a hole 3%} of larger diameter than the hole 29 is drilled in axial alignment with hole 29 into the top of the handle, hole 350 being screw threaded so as to be closed by a removable closure plug 31 for permitting ready access to, or removal of, the valve assembly for servicing. A sealing gasket 32 is confined between the head of the plug 31 and the counterbored seat 33 to prevent escape of air from the valve chamber 26.

For simplicity in manufacturing, at its upper end valve 27 has a reduced portion 27b (Figs. 5 and 6) which serves as a rivet to secure to the top of the valve a valve seal retainer 270 in the form or" a washer. Confined between jthe Washer 27c and an enlarged head 27f of the valve 27 is a valve seal 27e, preferably of Neoprene or other suitable flexible material. The upper face of the enlarged head 27f of the valve stem is provided with a peripheral upwardly projecting annular flange or rib 27;; which serves in the nature of a reaction support about which peripheral portion of the Neoprene seal 27c may be flexed by the air under pressure in chamber 26 from the position shown in Fig. 5 to the position shown in Fig. 6 during the initial opening movement of the valve and thus maintain momentarily the peripheral edge of the sealing washer 27s in contact with the valve seating surface 28s on the upper face of valve bushing 28. At its lower end the main stem portion 27a of valve 27 which projects downwardly beyond the lower end of the bushing 28 is provided with a rounded face 27/2 for engagement by a trigger 35 ivoted, When the valve 27 is raised sufiiciently to break the seal between the edge of Washer 270 and seat 280 the air pressure in chamber 26 will engage the bottom face of washer 27c and flip and hold V the peripheral portion of the valve up against the under face 27d of retainer 270, thus permitting free flow of air from chamber 26 past valve 27. The valvebushing 28 is provided at its upper end with an enlarged bore or chamber 28:? into which the air is freely admitted from the valve chamber 26 when the valve 27 is raised entirely as its seat. This air under the pressure which has built up in the expansion chamber flows from the chamber 28d through port 23b into the conduit 37 which communicates at its end with an annular passage 38 that communicates through longitudinal passages 39 (Figs. 1 and 7) in the cylinder closure cap 40 to the mace above the top of air piston 50.

The intermediate portion 27i of the valve stem is smaller in diameter than the bore 28a of the valve bushing to form a metering opening or passageway for exhaust air flowing from conduit 37 through port 23b in the valve bushing 28 to port 28c thereof which leads to atmosphere for exhausting air from the cylinder and piston. The handle casting 20 has a boss portion 41 which is bored out to receive a cylinder 4-2 that is a slip fit in the bore of the boss 41. An annular rib 43 formed on said cylinder intermediate its ends is adapted to seat against a countersunk portion 44 machined on the lower surface of the boss 41 and to hold the cylinder 42 against movement when the cylinder cap 40 is screwed home onto the screw threads 45 provided at the upper end of cylinder 42 against a countersink 41a in top of boss 41. The cap 40 has formed therein a plurality of air passages 39 (Fig. 7) that are open at their lower ends (Fig. 1) to the annular passage 38 in boss 41. At its lower end the cylinder 42 is provided with interior screw threads 46 to receive the upper reduced threaded end 47 of an adapter 48, having a cup portion 432, the purpose of which will be hereinafter more fully described.

A piston 56 is slidably mounted within the bore 51 of u the cylinder 42 and is normally held in its uppermost position by a coiled compression piston return spring 53. The top 56a of the piston is fiat so as to make a close sealing lit with the inner fiat face of the closure cap 40 as shown in Fig. 1 of the drawings. An important feature of the construction of the piston is that it is provided around its peripheral outer edge with a chamfer 50b which has to be at a very definite angle so as to deflect the air which enters into the closure cap through the longitudinal passageways 39 therein and break the seal between the piston and under-surface of the cap 40 after the air pressure has built up inside the cap to a predetermined amount sufiicient to break the seal.

We have found after a long period of experimentation that it is absolutely essential in order to obtain an effective operation of the air cylinder and piston that the piston must move after it has started its downward travel with a high velocity so as to obtain a quick, snappy driving action of suflicient speed to cause the staples to be driven cleanly through the material to be fastened in place. In

this connection the delayed full opening of valve 27 together with the provision of the chamfer 50b at the top of the cylinder is of the utmost importance, in conjunction with the flat sealing contact of the flat top 50a of the piston with the under side of the cylinder cap 40 which also cause the piston to hesitate momentarily during the initial opening of valve 27. We have found that by varying the angle of the chamfer 59b between 10 and 40 to the side walls of the piston the time interval of the pistons hesitation may be accurately controlled. As the air pressure builds up, the piston hesitates slightly and then starts its travel downwardly until the driver contacts with the staple to be driven by which time the piston has speeded up and is traveling with a relatively hig velocity;

We have also found, as a result of our experiments, that in order to obtain the requisite snappy action of the piston it is essential to provide the piston with a plurality of peripheral grooves 590, which not only serve to carry the lubricant along the cylinder bore but also seem to act somewhat in the nature of piston rings to more effectively prevent by-passing or escape of air between the skirt of the piston and the cylinder bore 51.

As shown in Fig. l the piston 50 is cup shaped as indicated at 500. Received within the cup-shaped portion nitrates 50a of the cylinder is a cup-shaped bumper retainer 55 having a peripheral shoulder or flange 56 at its upper end. The flange 56 serves as an abutment seat for the top coil of the piston return spring 53 while the outer surface of the cup-shaped portion of the retainer 55 serves as a locating means for the top coils of said spring, the bottom coils of which are centered by their engagement within the cup portion 482 of the adapter 48. Mounted within the interior of the bumper retainer 55 is a bumper or shock absorber 57 of rubber or other suitable resilient or yielding material. The top wall of the bumper retainer 55 is provided with an aperture 58 shaped to conform to the configuration of a driver 6%.

As shown in Fig. l, the top face of the bumper retainer 55 is flat and seats against the inner flat face of the cupshaped portion 50d of the piston 59 and the aperture 58 in the top portion of the retainer 55 is countersunk as indicated at 58a so that the enlarged head 69a of a driver 64) will be flush within the head portion of the bumper retainer 55, all as shown in Fig. l. The shank portion of the driver 60 is of approximately T-shaped configuration, as shown best in Fig. 7 of the drawing, having a pair of longitudinally extending ribs ilb one on each side thereof. These ribs 6% are shaped to fit neatly but slidably within a track 61 formed within a nose piece 62 as shown best in Fig. 8.

Mounted within the lower end of'the cylinder 42 and resting upon the reduced upper end 47 of the adapter 48 is a piston bumper in the form of a sleeve 7i) preferably of plastic or other suitable material; a washer 72 of steel preferably being interposed between the bumper and the top face of the adapter 48.

As many different size staples are used industrially, for example, to secure upholstery or other fabrics to foundation pieces in the automotive industry, the gun of the present invention consists of two separate units, a power unit, which comprises the handle 29 with the air cylinder 42, piston 50 and air valve assembly 27, 28 forming one unit and a staple strip magazine forming another unit.

Each magazine unit consists of a track section, together with a track cover and nose piece 62 which is designed for the particular size of staples for which the gun is to be used at any particular time; the driver 69, together with the nose piece 62 being proportioned and shaped in accordance with the size of staples to be driven.

In the exploded View of Fig. 9 of the drawing I have shown a nose piece 62, together with the track section and other parts that go to make up a magazine unit for the driving of narrow-crown staples. These narrow-crown staples for which the parts shown in Figs. 8, 9 and 10 are adapted to be used are approximately 1 of an inch between the staple prongs.

In accordance with the present invention we provide a pluralityof staple strip magazine unit assemblies which may be quickly and readily detached and attached from the handle section. The parts which go to make up a strip magazine unit per se comprise a screw-threaded adapter 48, a nose piece 62., together with a staple supporting track and a track cover which carries a staple strip pusher and the springs to actuate the pusher presently to be described. A magazine assembly includes in addition thereto, a driver 60, bumper retainer 55, a bumper or shock absorber 57, and a piston return spring 53, as hereinafter described.

As shown in Fig. 8 of the drawing, the nose piece 62 is provided with a guideway 64 into which fits the portion 63 of the driver 69. The nose piece 62 is also provided with a trackway 61 into which fit the longitudinal ribs 60b of the driver 69. At its upper end the nose piece is reduced, as indicated at 65 (Fig. 9) to receive a sleeve 12%) that serves as a stop against which the bumper 57 strikes when the piston reaches the end of its driving stroke, sleeve 12!) being seated on a shoulder a formed by enlarged part 66 of nose piece 62. It will, of course, be understood that the trackway 61 formed in the nose piece is so proportioned as to receive but one staple at a time which fits snugly but slidably therein to prevent spreading of the staple legs as the staple is driven into the material and that the trackway extends the entire length of the nose piece 62 and is open at both the top and bottom ends of the nose piece. understood that the lower end of the nose piece may be extended as far beyond the lower face of the track section as may be desired for reaching into otherwise inaccessible places.

The adapter 48 by'means of which themagizine unit is attached to the handle unit, as shown in Figs. 9 and 12 of the drawings, in addition to having the upper reduced serew threaded portion 47, has a pair of depending legs 48:; which are adapted to embrace the Widenedportion 67 of the nose piece and are suitably brazed thereto after the parts have been assembled.

The magazine section, as shown best in Figs. 9 and; 10

of the drawings, consists of a lower track section 75 having a pair of beads 76 on each side thereof that form longitudinal grooves which serve as a track for the flanges 80 extending laterally from the lower edges of the side walls of a track cover member 77 made of a sheet steel:

stamping bent into a general U-shaped configuration.

Secured, preferably by spot welding to the inner face of the bottom web of track section 75 is a track proper 78 which is of the proper size to fit between the legs of the staples to be driven; in this case, the narrow-crown staples.

Mounted on and brazed to the front end of the track section 75 is a jamb plate 79 which when the parts are assembled is adapted to abut tightly against the fiat face of the widened section 67 of the nose piece.

The cars 71 at the front end of track section 75 are adapted to straddle the side faces of the widened section 67 of the nose piece. In assembling the magazine unit the track section 75 with the ears 71 astraddle section 67 has the jamb plate 79 abutted against the flat inner face 'of the widened section 67 of the nose piece 62 and with the bottom of the jamb plate 79 resting upon the ledge 68 of the 'nose piece. The legs 43:; of the adapter 48 are then slipped down over and astraddle the ears 71,

with the turned portion 66 of the nose piece fitting neatly within the central hole 48c of the adapter.

For convenience in manufacturing, the underface, of the widened. flange portion 48b of the adapter has a couple of small holes drilled in it between the legs 48a and the hole 480 in which are placed small slugs of copper brazing material. The nose piece and track section, together with the adapter, are placed in assembled condition in a fixture so as to hold the nose piece at an exact right angle to the track section and, with the parts so assembled in the fixture, a light projection weld is made through the assembly at 480 (Fig. 9). Brazing material is then placed around the edges of the parts which are in contact and the unit is then placed in a heating furnace to braze the parts together in assembled condition. 7 As shown best in the inverted view Fig. 11 the track cover 77 contains a pusher 31 for pushing the clips of staples forward to the driving end of the machine. The pusher 81 is of U-shaped configuration so as to fit slidably over the top of the track member 78 shown in Fig. 9.

At their lower rearward ends the side walls of the pusher rear end thereof so as to project below the bottom wall of the track section 75 (see Figs. 1 and 11), is provided to facilitate moving the cover 77 to open position while the: rear face ofthewide section of the nose piece 62 formsastop with which the forwardextension 115' of;the top wall of the track cover engages to limit the forward It will be likewise.

travelofthe. cover section in its closed position and prevent it from extending into the trackway 61 of the nose piece 62.

An important feature of the present invention is the construction of the track section and the nose piece 62 at the point where the jamb plate 79 abuts the nose piece, As the staples must be fed longitudinally of the track andendwise laterally into the track portion 61 of the nose piece, the jamb plate 79 whichis welded to the track member 78 is provided with a U-shaped opening 70 through which the staples can be. fed laterally into the trackway 61 of the nose plate. opening 70 the jamb plate 79 is provided withinclined cam faces 79 c (Fig. 9') for directingthe prongs off the staples into the trackway 61,

For the pumose of. permitting the staples to enter laterally into the track section, the latter is relieved; or cut away, as indicated at 69 by an amount just sufficient to permit the staples to enter trackway 61 while leaving the side walls of the trackway 61' of the correct dimen sion to hold the staples against spreading as they are driven into the material with which they are to be used.

It will be noted that the attachment of the ends of' the lower runs of the springs 83 to the tabs 82 formed on the lower rear end of the pusher 81 causes the springs; to exert a downward pull on the back end of the pusher so as to cause the lower edge thereof to be held snugly in contact with the top face of the track 73 and thus hold the pusher in an inclined position as shown best in Figs.

1 and 15. This causes the lower end'of the front face of the pusher 81 to engage the bottom of the legs of the staples'to be fed and thus insure that the bottom legs of:

the staples will be fed into the track 61 of the nose piece. This together with the cam faces-79c will tend to prevent the legsof-astaple as it is severed from a strip thereof from being turned backwardly into the track section of the magazine unit, thus causing jamming of the staple strip feeding mechanism. 7

At-its rearmost end the track section 78 is provided with a downwardly inclined section which terminates at the rear end of-thetrackin a lug or shoulder 88 with which the rear-end of% the pusher 81 contacts to, serve to limit the opening movement of' the track cover 77 when it is pulled backwardly to insert a new strip of staples.

In the case of the narrow crown staples, the tabs 82 to which the ends of the springs 83 are secured project laterally outward sufficiently to engage the rims of the pulleys 84.so that when the track cover is moved to open position, it will pick up the pusher 31 and pull it to the rear end of the track 78. As the points'of'contact of these tabs withthe pulley rims serve as fulcrum points about-which the downward pull of the lower run of the springs 83 isexerted, therear end of the pusher will be held snugly against the topface of track 78 and thus insure the engagement of the rearend of the pusher with the. stops 88 (Fig. 15) at the top rear end of track 78 thereby to limit the opening movement of the track cover-77.

Secured to the top of the track cover 77 is a flat leaf spring: 89 which is provided intermediate its ends with a hump portion 94). and terminates in a finger tab 91 by means'of which the spring may be depressed. The hump 99 is adapted to engage behind a filling piece-92 brazed or otherwise secured to the inner face-of theweb of a yoke 93, the lower legs of which are attached to the side walls'of the track section 75, and thus lock the track coverin its closed position; the spring-89together-with an inclined surface 480? (Fig. 1) on the under side of the flange 48b of the adaptor 48 holding the cover down snugly against the lower track section 75' to insure a proper predeterminedclearance between the top of'the track 78 and the under. surface of the top wall of the track cover and thus permit free sliding movement of the staple strips and pusher 81 along track 78. Thefillingrpiece 9 2: alsozservesas a means-'for providingcthe necessary screw threads to receive a fastening screw 94 At the lower end of by means of which the rear end a of handle unit 20 is secured to the staple magazine unit to prevent the handle from rotating or swinging sideways out of line with the magazine unit when the device is in use.

In Figs. 3, l2 and 14 we have shown the parts of a magazine unit for wide-crown staples. As shown in Fig. 12, the parts which comprise the magazine for widecrown staples are essentially the same as shown in Figs. 9 to 11 for the narrow-crown staples, except there are differences in details of construction due to the difference in width of the staples to be fed. As shown in Fig. 12 the nose piece 62a is provided with a trackway 61a similar to the trackway 61 of the nose piece 62, except that it is, of course. wider for the wider crown staples. At its top end the nose piece 62a is provided with a reduced portion 65a which is of a diameter such that the flange of the cup-shaped end of the bumper retainer will pass over it when the latter is driven downwardly to execute a driving stroke, the top face of the nose piece serving as an abutment against which the lower face of the yielding bumper 57 strikes. Immediately below the reduced end a of the nose piece it is provided with a portion of larger diameter 66a adapted to fit within hole 480 of the adapter 48, and, just below the portion 66a, the nose piece 62a is provided with a widened portion 67a similar to the portion 67. The inner face of the widened portion 67a of the nose piece 62a is also cut away as at 69a to provide a ready entrance for the staples laterally into the trackway 61a of the nose piece.

Secured to the track section a for the wide crown staples (Fig. 12) is a track member proper in the form of a channeled shaped piece 78a, the lower wall or web of which is spot welded to the track section 75a. At its front end the channeled track 78a proper is closed by a jamb plate 79a suitably brazed to the legs of the channeled track 73a. The jamb plate 79a is provided with a pair of laterally projecting curved cam faces 79d (Fig. 14) similar to the cam faces 79c which serve to engage the lower prongs of a staple and direct them positively into the trackway 61a of the nose piece 62a as the staples are engaged by the driver to separate them from the strip of staples and force them downwardly into the material to be fastened.

The front end of the track section 75a is provided with a pair of ears 71a similar to the ears 71 shown in Fig. 9 which are also adapted to straddle the widened section 67a when the parts are assembled.

Due to the fact that the space between the prongs of the wider crown staples provide ample room for the housing of the spring 83a used for forcing the staple pusher 81a against a strip of staples, in the form for the wide crown staples shown in Figs. 4 and 12 to 15 only a single spring 83a is used. This spring 83a has its rearmost end secured to a tab 85a struck from a spring housing member shown best in Fig. 4, while the spring intermediate its ends is coiled about a single sheave or pulley 84a. The forward end of the spring is fastened to a tab 82a formed or struck out from the rear end of a horizontal web that connects the side walls 126 of a U-shaped piece 130 welded to the inner face of the top wall of the U-shaped pusher member 81a as shown in Fig. 16.

After the spring 83a is assembled in the spring housing 90 as just described the hooked end 91 of the housing'90 is hooked through the slot 92 in the rear end of the track cover 77:: (Fig. 4); the engagement of the rear face of the hooked end 91 with the rear end of the track cover 77a preventing movement of the spring housing 90 longitudinally of the cover. The extended ends 1100 of the shaft portion of the sheave 84a engage the angular surfaces 11017 at the front ends of side walls 126 when the track cover is moved rearwardly and thus carries the pusher 81a with it. The shaft ends 1100 also serve as abutment stops against which the angular surfaces 1101) (Fig. 16) of the pusher 81a abut when the track cover is pulled back to its full opened position and as fulcrum points against which the pull of the lower run of spring 83a is exerted to hold the rear end of the pusher snugly against the top face of track 78a and thus insure engagement of the rear end of the pusher with the stops 88a (Fig. 3) thereby to limit the opening movement of the track cover 77a.

As shown in Fig. 18, the pitch line for the sheave 84a for the single springs 83a is so arranged that the coils of the springs at their lowermost end will be forced into close contacting engagement with adjacent co ls and thusprevent the formation of a space at the point where the coils contact with the sheave that would permit them to become engaged or hooked over the sheave in such way as would prevent the free travel of the spring over the sheave- As shown in Fig. 20 the construction and arrangement of the tab 82a on the pusher element 81a is such that there is suflicient space between the ends of the tab and the body of the material from which it is struck out to permit the two terminal coils with which the spring 83a is provided to slip readily under the tab when the spring is held at a right angle to the pusher but which space is insufiicient to permit the two coils to pass through it and thus become accidentally detached from the tab when the body of the spring lies in its horizontal operative position as shown in Fig. 4.

The track section for the wide-crown staples is assembled to the nose piece 62a and adapter 48 in a fixture and then the parts are brazed together as hereinbefore described.

After the track section for either the wide-crown or narrow-crown staples has been properly assembled to the nose piece, either 62 or 62a which goes with the particular track section, in the fixture provided for such purpose, and the parts have been integrally united together as a unit by spot welding and brazing as hereinbefore described, the track cover for the particular size staple is then placed over the track section proper, with the pusher 81 or 81a, as the case may be, held in place by the fingers of the person doing the assembly work, the pusher is engaged over the respective track 78 or 78a, and the cover is slid home until the end of the cover 77a for the narrow-crown staples abuts against the nose piece or an abutment piece 111 brazed to the top wall of the cover 77 for the wide-crown staples abuts against flange 43b of the adaptor 48 (Fig. 17). When this occurs, the hump 96 of the spring 39 engages behind the filling piece 92, as shown in Fig. 1 of the drawings and the inclined rear face of the spring hump will force the cover forwardly and hold it in snugly locked position.

In order to facilitate the loading of a new strip of staples on the staple track 78 or 78a, a major portion of the side walls of both the narrow crown track section 75 and the wide crown track section 75a is cut away above the beads 76 and 76a from points adjacent to their front and rear ends, thereby to expose the tracks 78, 7 8:: when the track covers are slid to their fully opened position.

It will be noted that in the case of both the narrowcrown and the wide-crown staples that after the track cover 77 or 77a with the respective pusher 81 or 81a together with the pusher spring 83 or springs 83a respectively assembled therewith has been placed on the track section the cover may be moved to opened or closed position without disturbing the unitary assembly of the track section to the nose piece and adapter. When a new strip of staples has been placed on the staple track 78 or 78a the front end of the pusher engages the rear end of sai strip and as the cover is pushed forwardly to its closed position the pusher will be held, by its engagement with the rear end of the staple strip, towards the rear end of the track unit, thus causing the springs 83 or 83a to be stretched and moving the pulleys 84 or 84a forwardly out of contact with the pusher. When however the cover is moved to its opened position the pusher 84 or 84a will be pulled rearwardly by the cover, as hereinbefore described, whiie the rear end of the pusher will be held snugly but yieldingly by the pair of springs 83f or the single spring 83a, as the case may be, against the top face of 'the track 73 or "73av to insure its engagement with the stops 83 at the rear end of the track and limit the opening movement of the track cover. If it is desired to remove the track cover 77 entirely this may be readily accomplished by inserting a small screw driver or the like and lifting the rear end of the pusher against the action of the spring 83 so as to permit it to clear the stop 83.

A driver 69 of the correet size and shape to go with the staples of the size for which the magazine unit is to be used is then inserted into the bumper retainer with which his intended to be used, the driver bumper 57 first having beeninserted into the cup-shaped cndof the retainer 55. A collar 12% is thenplaced over the end 65 of the nose piece and piston return spring 53 then has its lower end inserted into the cup-shaped end of the adapter 48' and with the lower coils thereof encircling the collar llfion the top of the nose piece. The

driver assembly consisting of the bumper retainer 55 and driver bumper 57 is then assembled to the magazine unit by inserting the lower end of the driver 6i? into the trackway of the nose piece 615 or 62a.

1% in the lower end of the driver 69 reaches a position below the lower face of the adapter substantially as shown in Fig. 17 of the drawing. The hooked end 101 of a spring clip 102 is then engaged within the notch 190 of the driver and the lower upturned end 103 of the spring clip is placed within a longitudinal slot 104 formed centrally in the lower part of the driver 69. The upward thrust exerted by the piston return spring 53 forces the driver 60 upwardly and thus holds the top end 101 of the spring clip 102. upinto the hole 480 of the adapter, 1

head 55 and adapter 43, may then be engaged with a handle or power unit 2% by screwing the threads on the reduced end 47 of the adapter intothe threads 46 formed in the lower end of the cylinden $2, and the assembly is screwed home until the upperface of the flange 48d of the adapter is firmly seated against the lower face of the cylinder 42. The cylinder closure cap which is then backed off a turn or so permit the rear end of the magazine unit to be rotated'into alignment with the rear. end 29:: of the handle of the power unit, and the screw 94 is then screwed'into position to hold the endIZOa of the handle from rotating and, with the handle secured in proper vertical alignment with the magazine unit,

the cylinder cap 49 is then tightened firmly in position. We have found after a long period of experimental development that the sealing contact provided between J the flat upper face 553a of the piston 50 and the lower fiat inner surface of the cylinder closure cap is of the utmost importance likewise the angle of the chamfer 5%. so that a momentary hesitation of the pistonwill occur.

sufiicient to perrm't the air pressure to build up above. the piston and thereby insure a positive sharp, quick. driving action of the piston as it travels downwardly on its working stroke.

As will be seen fromFig. lot the drawings, the driver 66 and piston have an appreciable amount of travel before the lower end or" the driver engages a staple to disengage it from the staple clip and force it into the,

material to be. stapled.

Wehave also found it to be imperative if excessive breakage of the driver 6% is to be avoided that some After this has. been done the spring 53 is compressed by pressing downwardly' upon the top of the retainer 55 until a notch shock absorbing or snubbing means he provided to relieve the drivers from the sharp impact or blow which occurs when the lower face of the skirt of the piston 50 engages with the relatively hard bumper sleeve 70. For this purpose we have provided the rubber bumper member 57 which is so proportioned and arranged within the retainer 55 that the lower end of the bumper will driver 60 from the sharp impact of the blow of the piston against the bumper 70.

When it is desired to change the gun for use with a different size staple the magazine assembly which had been employed is detached from the power unit as follows: The driver 61) is driven to the extreme lower end of its travel and by holding the valve 27 open driver 68 is held there. 191 engaged within the notch of the driver and in engagement with the adapter and with the upturned lower; end 103 of the clip in slotliid' in nose piece 69. The trigger 35is then releas ed'and' piston spring 53 will draw the driver 60 snugly up into locked position. The screw 94' at the rear end of the handle 20 is then removed, cylinder cap 40 is loosened and the magazine assembly is then detached from the power unit by rotating it relatively to the handle to unscrew the threaded portion 47 of the adapter from the screw threads 46 in the bottom of the cylinder 42; A new magazine assembly is then screwed into the cylinder until the flange 43b of its adapter. 48 is seated firmly against the lower face of the cylinder. oil? to permit the handle and magazine units to be properly aligned, the screw 94'is then inserted and the cylinder cap firmly tightened. V

The manner in which the device operates is'asfollow s:

The handle being. attached to a source of compressed air by means of hose 24', air under pressure from said source enters through the bushing 21 into the air expansion or accumulator chamber 25 from whence it flows into the valve chamber 26 to be immediately available for use when the valve 27 is opened.

When the operator wishes to drive a staple, he raises the trigger 35 so as to cause 'it to engage with the rounded lower end 27% of valve stem 27a. and thus raise valve 27; 7 During the initialupward movement of the valve 27 the under pressure in valve chamber 26 will enter between the lower face of. the valve seal retainer 2'56 and the sealing washer 27e thuscausing the outer peripheral portion of the washer 27e to flex downwardly from the position shown in Figure 5 to that shown in Figure 6 andthereby maintainits seal with the seat 2312 on the upper face of the valve bushing 28. During this initial opening movement of the valve the sealing engagement ofithe peripheral edge of the washer 27:; with the seat 2Se is maintained until annular groove 27 (Fig. 1) of the valve stem passes above the exhaust port 280 in the valve bushing 28. After this occurs, air which flows from the'valve chamber 26 into the bore 28d ice the valve bushing willengage theunder face of the washer 21a and flap it up into engagement with the. under surface 27d of the valve head 270 thus breaking the seal between the peripheral edge of the Washer 272 and the valve seal 28s. This. permits the air to flow freely into the bore 28d, of the valve bushing 28; At t e same time this occurs the stem portion 27a of the valve 27' closes the exhaust port 280- and prevents the air which enters chamber 280! from passing out of'the exhaust port 280. The air under pressure which enters bore 28d of the bushing 23' then flfows through the port 285 into the conduit 37' and thence through annular- A. locking clip 192 has its upper end" The cylinder cap 40 is then backed 13 chamber 38 in the cylinder to the longitudinal passages 39 in the cylinder closure cap 46. This air under pressure builds up within the cylinder closure cap 40 until it passes the chamfered edge of the piston and breaks the seal between the top fiat face of the piston 5t) and the flat inner face of the cap and thus starts the piston to travel downwardly in a driving stroke.

Upon the first stroke of the gun to drive a staple, the notch 100 of the driver passes downwardly so as to release the hooked end 101 of the clip 102 from its engagement with the notch 160 in the driver 60 and hole 480 of the adapter, and the clip 102 then falls from the gun, thus permitting the piston, driver and driver head to be pushed upwardly by the piston return spring 53 until the flat face 59a of the piston engages with the inner flat surface of the cylinder closure cap 40.

It will be understood that the clip 102 is used only for the purpose of holding the driver and the piston return spring 53, together with the bumper retainer 55 and bumper 57 in assembled condition, with the track section of a magazine unit for the ready attachment of such assembled parts to a combination handle and power unit. As heretofore pointed out, due to the fact that the invention contemplates the use of diiferent sized magazine unit assemblies for use with the size staples for which the gun is to be employed and as each magazine unit when assembled consists of the track section permanently secured as by brazing to an adapter 48, the nose piece 62, a driver 63 with piston return spring 53,

bumper retainer 55 and bumper 57 and as these parts are held in assembled condition by the clip 102 as just described, the assembled magazine unit may be kept in a storeroom or any suitable place until needed for use.

It will, of course, be understood that the driver 60 moves downwardly an amount sufiicient to drive the staple which has been detached from the strip thereof through the material to be fastened.

After the staple has been removed from a strip thereof and driven home, the operator releases trigger 35 thus permitting valve 27 to drop by pressure being exerted upon the top face of valve seat retainer 270 thus shutting off the air flow to piston 50 and permitting the piston return spring 53 to force the piston 50 upwardly. During the upward travel of the piston the air which has accumulated above the top of the piston is now forced outwardly through the longitudinal passages 39 of the cylinder closure cap 40, the annular passage 38 and into the conduit 37, flowing from said conduit and thence through the port 28b into the chamber 28d of the valve bushing 23 and around the annular metering passage provided between the bore 28a of valve bushing 28 and the stem 27 of the valve 27 and out to atrnosphere through the exhaust port 280. As heretofore pointed out, the stem portion 271' of the valve 27 is slightly smaller in diameter than the bore 28 of the valve bushing to provide an annular metering passageway through which the exhaust passes to the exhaust port 230. This serves to cushion the return stroke of the piston and avoid any hammering action by the piston on the inner surface'of the cylinder closure cap 48 which would otherwise tend to be quite destructive.

As the staples are detached one by one by the driver 6t) from the strip of staples in the magazine unit, the staple pusher 81 under the tension of springs 83 will feed the strip of staples so that the outermost staple of the strip will pass laterally into the opening 69 relieved in the nose piece 62 until the outermost staple lies within the trackway 61, in position to be engaged by the driver 63 on its next downward stroke.

As each staple is severed from the strip thereof the lower ends or prongs of the staple legs will engage with the cam lugs 79c (Fig. l) or 79d (Fig. 14) on the jamb plate to insure that the staple legs will be forced outwardly and positively into the track 61 of the nose piece, thus preventing the legs or prongs of the staples:

after which the track cover 77 is shoved forwardly until 14 from turning backwardly into the track section of the magazine unit and cause jamming of the latter.

For the purpose of preventing a staple pusher from being fed into the path of the driver 60 after the last staple of a strip thereof has been fed and the staple supply is exhausted, the forward ends of the pushers 84, 34a are provided with a pair of small outwardly extending ears or tabs 110 (Figs. 3 and 10) which engage the inner face of the nose piece and prevent the pusher from being pushed outwardly by the pusher springs into the trackway and in the path of the descending driver. In the wide crown pusher (Fig. 16) the surfaces 110a are provided to supplement the tabs 110 and having as a bumping surface, the back surface of jamb plate 79a (Fig. 14).

When the last staple of a strip has been driven, the operator may grasp the projecting finger piece 91 of the spring 39 and depress it until the hump 90 of the spring is flexed below the filler piece 92. The operator may then pull the track cover section 77 rearwardly until the pusher 81 engages the stops 88 provided at the rear end of the track 78 and until the parts are in the position shown in Fig. 15; the engagement of the pusher 81 with said stops limiting the outward movement of the track cover. In this extreme outward open position of the cover 77 or 77a the cover will be supported only at its innermost end by the engagement of the pusher 81 or 81a with the stops 88 or 88a; hence, the weight of the outwardly extending, overhanging major portion of the cover will tend to hold the cover in its fully open position. A new strip of staples may then be inserted,

the abutment 111 in the case of the wide crown staples engages the flange 48b of the adapter 48; the forward stop for the narrow crown is the foremost end of track cover 77-stopping against the nose piece 62 (Fig. 9).

An important feature of the bumper is that, if the valve 27 is held open at any particular time, the engagement of the lower face of the skirt of the piston with the upper face of the bumper 70 serves as a seal to prevent undue escape of air that bypasses the piston, but to permit suflicient air to escape to prevent back pressure.

The construction and arrangement of the valve 27 by means of which the delayed opening action of the valve, as hereinbefore described occurs, together with the fiat sealing contact between the top of the piston 50 and the inner face of the cylinder closure cap 49 cooperate to insure the delayed action of the piston during the time the air pressure builds up within the cylinder closure cap and until the sealing action of the piston with'the cylinder cap is broken by the passage of the air that passes the chamfered edge 5% of the piston.

The track covers are provided with an observation opening 125 adjacent the adapter 48 so that the operator may readily inspect for the presence or lack of staples on the staple track or to see if the nose piece 62 is open in the front and clear any staples which may have become jammed in the track section.

It will be noted that there is but a single driving member, namely, the driver 69, interposed between the piston and the staples and that the driving force is imparted to the driver through the engagement of the enlarged head 60a of the driver with the flat under face of the top wall of the piston.

It will also be noted that with each form of magazine unit shown, the ears 71 or 71a at the front end of the side walls of the track sections 75, a, respectively, are confined, or, in effect, clamped between the solid metal of the wide part 67 or 670: of a nose piece 62 or 62a and the relatively thick legs 48a of the adapter so that an 'mterlocked strong engagement of the parts is effected whereby the parts mutually cooperate to brace each other and form a strong rigid unit when brazed together as hereinbefore described.

While we have described and illustrated a satisfactory 15 constructional example of 'our'invention for'use with staples that has proven highly satisfactory in actual commercial use, it will, of course, be understood that the invention may be employed for driving tacks, brads, rivets or other fastening devices by modifying the magazine units, drivers and nose pieces accordingly and 'many other changes, variations and modifications within the skill of the art may be resorted to without departing from the spirit of the invention as set forth in the claims hereunto appended in which the term staple is to be construed to include tacks, brads, hollow rivets or other fastening devices capable of being made in interconnected form for use with an air gun constructed in'accordance with the principles of the present invention.

We claim: 1. In an air gun for driving fastening devices such as stapls, tacks, brads or the like, an air cylinder, valve means for admitting air from a source of air under pressure to said cylinder, a piston slidably mounted in said cylinder, a driver in contacting engagement with said piston for engaging the fastening devices to be driven, a nosepiece in'which said driver is slidably mounted, and resilient shock absorbing means interposed between said nose piece and said piston for contacting shock absorbing engagement with said nose piece when said piston reaches the end of its driving stroke.

2. In anair gun for driving fastening devices such as staples, brads, tacks, or the like, an air cylinder, valve means for admitting air from a source of air under pressure to said cylinder, a piston slidably mounted in said cylinder, a nose piece having a trackway dimensioned to receive a fastening device to be driven, a driver having its lower end slidably mounted in the trackway of said nose piece and its upper end in engagement with said piston, a bumper retainer interposed between said nose piece and piston but freely movable axially of said piston, and yielding shock absorbing means carried by said retainer, interposed between said nose piece and piston for contacting shock absorbing engagement with said nose piece when said piston reaches the end of its driving stroke thereby cushioning the impact of said piston on said driver.

3. In an air gun for driving fastening devices such as staples, brads, tacks or the like into materials to be fastened, a magazine unit consisting of a track section hav-' said devices one by one into the trackway of said nose piece, a headed driver having its lower end slidably fitted into and carried by the trackway of said nose piece, a screw threaded adapter integrally united with said nose piece and track section, a bumper retainer and resilient bumper means mounted therein carried by the upper end of said driver and a coiled compression piston return spring confined between said retainer and adapter for returning the piston hereinafter set forth after ithas performed a driving stroke a single power unit for detachable engagement with said magazine unit and comprising a main body having a handle portion, an air cylinder in said body, a piston slidably mounted therein, means for connecting said handle to a source of air under pressure, and valve means interposed between said source of air and said cylinder for admitting air under pressure to said cylinder to cause said piston to perform a driving stroke, said cylinder being provided with screw threads with which said adapter may be engaged to unite said power unit in hssembled operative relationship with said magazine unit.

4. An air gun as set forth in claim 3 in which means additional to said adapter are provided for locking said magazine and power units against relative rotation when assembled.

5. An air gun as set forth in claim 3 in which means are provided for securing said magazine unit and power unit in assembled relationship, said last-named means comprising a cylinder closure cap in screw-threaded engagement with the upper end of said cylinder for securing said cylinder to said handle.

6. An air gun as set forth in claim 3 in which means are provided for securing said magazine unit and power unit in assembled relationship, said last-named means comprising a cylinder closure cap in screw-threaded engagement with the upper end of said cylinder for securing said cylinder to said handle against said adapter, and a single screw for fastening the rear ends of said magazine unit and said handle to prevent relative rotation thereof and disengagement'of the screw threads of said adapter and cylinder of said power unit.

7. An air gun as set forth in claim 3 in which means additional to said adapter are provided for locking said power unit and said'magazine unit against relative rotation after they have been assembled, comprising a single screw passing through the rear end of said handle portion of said power unit and means integrally united with the rear end of said track section in which said screw is threaded thereby to clamp the rear ends of said handle portion and track sections together and cause them mutually to brace and reinforce each other.

8. In a stapling or tacking machine, a staple magazine and feed structure comprising a track section of inverted U -shaped cross-section having a bottom wall with a front edge and side walls projecting forwardly of said front edge to form a pair of forwardly projecting laterally spaced cars, a nosepiece having a staple-receiving trackway formed therein and a portion of rectangular crosssection mounted between said ears with the side walls of said portion in contacting engagement with the inner faces of said ears, and a screw-threaded adapter having a pair of laterally spaced depending legs straddling said cars in contacting engagement with the outer faces thereof whereby said ears of said track section are clamped between and reinforced by said nosepiece and said legs.

9. In a stapling or tacking machine, a staple magazine and feed structure comprising a track section of inverted U-shaped cross-section having a bottom wall with a front edge and side walls projecting forwardly of said front edge to form a pair of forwardly projecting laterally spaced ears, a nosepiece having a staple-receiving trackway formed therein and a portion of rectangular cross-V section mounted between said ears with the side Walls of said portion in contacting engagement with the inner faces of said ears, and a screw-threaded adapter having a pair of laterally spaced depending legs straddling said ears in contacting engagement with the outer faces thereof whereby said ears of said track section are clamped between and reinforced by said nosepiece and said legs and a joint of fused material connecting the contacting areas of said ears, said legs, and said nosepiece to unite said track section, said nosepiece and said adapter in a rigid unitary structure;

foremost staple thereof to be fed laterally into said trackway, and means for detachably'securing said assembly to a power unit having an air actuated piston for causing said staple driver to perform a staple driving stroke and said piston return spring being adapted to return said 17 piston and staple driver after the performance of said driving stroke.

11. A portable pneumatic gun for driving fastening devices such as staples, brads, tacks or the like into materials to be fastened, comprising a unitary power unit assembly consisting of a main body having a handle portion and a bore, an air cylinder having screw threads at each end thereof in said bore, a cylinder head in screwthreaded engagement with one end of said cylinder, a piston slidably mounted in said cylinder, means for connecting said handle portion to a source of air under pressure, valve means for controlling admission of air to said cylinder to cause said piston to be moved away from said head to perform a driving stroke, a magazine unit assembly for holding a supply of said devices and consisting of a track section having a track dimensioned to accommodate fastening devices of a predetermined size and shape, a nosepiece integrally united to said track section and having a trackway adapted to receive a single one of said fastening devices and guide its pointed end into the material to be fastened, means carried by said track section for feeding said devices one by one into said track- Way, a driver having an enlarged head at its upper end for simple contact driving engagement with said piston and having its lower end slidably fitted into and carried by said trackway, means for detachably securing said power unit and magazine unit assembly together in cooperating Working relationship comprising a screwthreaded adapter for engagement with the lower end of said cylinder integrally united to said track section and nosepiece, said magazine unit assembly including a cupshaped bumper retainer carried by said upper end of said driver for engagement with said piston, resilient bumper means mounted Within said bumper retainer for yielding shock absorbing contact with said nosepiece, and a coiled compression piston return spring confined between said bumper retainer and said adapter for normally holding said piston in engagement with said cylinder head.

References Cited in the file of this patent UNITED STATES PATENTS 1,045,619 Schweizer Nov. 26, 1912 1,700,052 Holman Jan. 22, 1929 1,739,338 Wadsworth Dec. 10, 1929 1,939,632 Randall Dec. 12, 1933 2,066,157 Pankonin Dec. 29, 1936 2,240,911 Polzer May 6, 1941 2,251,833 Polzer Aug. 5, 1941 2,311,412 Pankonin Feb. 16, 1943 2,340,717 Vogel Feb. 1, 1944 2,345,267 Keil Mar. 28, 1944 2,358,317 Crosby Sept. 19, 1944 2,430,321 Anstett Nov. 4, 1947 2,445,674 Kendall July 20, 1948 2,501,564 Goodstein Mar. 21, 1950 2,522,931 Curtiss Sept. 19, 1950 2,538,133 Tratzik Jan. 16, 1951 2,558,403 Wandel June 26, 1951 

